For the VoIP connecting to the PSTN, echo with the voice communication has
been a problem hard to solve and inevitable . Asterisk has a range of software-based
Open Source echo cancellation routines that are moderately effective in
eliminating the echo. However, there are cases in which these algorithms are not
effective.
To solve this problem, ATCOM offers a line of DSP-based echo cancellation
modules for all the digital (T1/E1/J1) cards with the EC series modules.